U.S. patent number 5,555,255 [Application Number 08/448,425] was granted by the patent office on 1996-09-10 for surface-emitting laser diode.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Erich Gornik, Anton Kock.
United States Patent |
5,555,255 |
Kock , et al. |
September 10, 1996 |
Surface-emitting laser diode
Abstract
A surface-emitting laser diode with an active layer (3) between
contact layers (2, 4) and reflector arrangements (9, 19) provided
for a vertical resonance condition, in which the surface of the
semiconductor material is provided with a spatial periodic
structure, which is intended for the excitation of surface plasmon
polaritons, and is covered with a thin metal film (5).
Inventors: |
Kock; Anton (Munchen,
DE), Gornik; Erich (Munchen, DE) |
Assignee: |
Siemens Aktiengesellschaft
(Munich, DE)
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Family
ID: |
6474323 |
Appl.
No.: |
08/448,425 |
Filed: |
June 5, 1995 |
PCT
Filed: |
November 24, 1993 |
PCT No.: |
PCT/DE93/01113 |
371
Date: |
June 05, 1995 |
102(e)
Date: |
June 05, 1995 |
PCT
Pub. No.: |
WO94/13043 |
PCT
Pub. Date: |
June 09, 1994 |
Foreign Application Priority Data
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Dec 3, 1992 [DE] |
|
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42 40 706.0 |
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Current U.S.
Class: |
372/96;
372/46.01 |
Current CPC
Class: |
B82Y
20/00 (20130101); H01S 5/18386 (20130101); H01S
5/0622 (20130101); H01S 5/18355 (20130101); H01S
5/34313 (20130101); H01S 2301/18 (20130101) |
Current International
Class: |
H01S
5/183 (20060101); H01S 5/187 (20060101); H01S
5/00 (20060101); H01S 5/10 (20060101); H01S
5/062 (20060101); H01S 003/19 () |
Field of
Search: |
;372/96,92,46 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
0395315 |
|
Oct 1990 |
|
EP |
|
0442002 |
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Aug 1991 |
|
EP |
|
Other References
Y Suematsu et al., "Advanced Semiconductor Lasers", Proceedings of
the IEEE, vol. 80, No. 3, Mar. 1992, pp. 383-397. .
E. Gornik et al., "Surface Plasmon Enhanced Light Emission in
GaAs/AlGaAs Light Emitting Diodes", Proceedings SPIE, vol. 1362
Physical Concepts of Materials for Novel Optoelectronic Device
Applications II: Device Physics and Applications (Oct., 1990), pp.
1-13. .
Japanese Abstract, "Semiconductor Light Generator", JP 60-123084,
vol. 9, No. 280 (E-356) (2003) Nov. 8, 1985..
|
Primary Examiner: Davie; James W.
Attorney, Agent or Firm: Hill, Steadman & Simpson, A
Professional Corporation
Claims
I claim:
1. A surface-emitting laser diode, comprising;
semiconductor material,
an active layer in said semiconductor material,
contacts on said semiconductor material for applying an operating
current to said surface-emitting laser diode,
a spatial periodic structure on a surface, facing away from the
active layer, of the semiconductor material,
a metal film applied at least to a region of the surface that is
provided with said spatial periodic structure,
said spatial periodic structure being of a height and a length of
each period and a minimum distance of said metal film from the
active layer and a thickness of the metal film being dimensioned
such that, during operation of the laser diode, surface modes are
excited at the surface, facing away from the active layer, of the
metal film by photons produced in the active layer, and
a reflector arrangement for forming a vertical resonator being at
least one layer on a side, facing away from said spatial periodic
structure, of the active layer.
2. A surface-emitting laser diode as claimed in claim 1, further
comprising:.
a further reflector arrangement between the active layer and the
metal film.
3. A surface-emitting laser diode as claimed in claim 1, wherein
the vertical resonator is bounded by the reflector arrangement and
by the metal film.
4. A surface-emitting laser diode as claimed in claim 3, wherein
the active layer is arranged between said contact layers which
adjoin said active layer vertically with respect to the layer
plane, and further comprising:
a covering layer between one of said contact layers and the metal
film, said spatial period structure being formed in said covering
layer.
5. A surface-emitting laser diode as claimed in claim 1, wherein
said contact defines a recess, and the metal film being in said
recess of said contact.
6. A surface-emitting laser diode as claimed in claim 1, wherein
said metal film forms said contact.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface-emitting laser diode
having a particularly good directional characteristic with
utilization of the excitation of surface plasmon polaritons.
DESCRIPTION OF THE RELATED ART
A surface-emitting, radiation-producing semiconductor component,
which is operated by means of excitation of surface plasmon
polaritons, is described in European Patent Document EP-A-0 442
002. This component can be configured, in particular, as a laser
diode. The structure is based on an emission mechanism by means of
excitation and emission of surface plasmon polaritons, these being
transverse electrical (TE) or transverse magnetic (TM) surface
modes, which can propagate at the interface between two different
media. With a suitable periodic structure of the interface, these
modes can be excited using electromagnetic waves. The properties of
light-emitting diodes, in particular laser diodes, can be improved
using this emission mechanism. Loss mechanisms, which appear in
conventional light-emitting components and limit the efficiency,
can thus be avoided, at the same time the line width being
considerably reduced and the external quantum yield being
drastically increased. Directed radiation with a defined
polarization can be achieved with a beam divergence of less than
6.degree.. In this case, a spatial periodic structure of the
surface of the semiconductor material, that is to say the
semiconductor surface facing away from a substrate over which there
is growth, and a thin metal film applied thereto are essential for
the design of this structure. The surface modes are excited at the
surface, facing away from the semiconductor material, of this metal
film, with the result that light is radiated in a directed manner
from the surface. The polarization direction results from the
direction of the periodic arrangement of the surface
unevennesses.
SUMMARY OF THE INVENTION
It is the object of the present invention to specify an improved
surface-emitting laser diode having intense beam focusing and an
adjustable radiation direction.
This and other objects and advantages of the invention are achieved
by means of the laser diode made of semiconductor material with an
active layer and with contacts for applying an operating
current,
in which the surface, facing away from the active layer, of the
semiconductor material is provided with a spatial periodic
structure,
in which a metal film is applied at least to a region, provided
with the spatial periodic structure, of the surface,
in which the height of the spatial periodic structure and the
length of each period of the spatial periodic structure, the
minimum distance of the metal film from the active layer and the
thickness of the metal film are dimensioned such that, during
operation of the laser diode, surface modes are excited at the
surface, facing away from the active layer, of the metal film by
photons produced in the active layer, and
in that the reflector arrangement for forming a vertical resonator
is present as a layer or as a layer sequence on the side facing
away from the spatial periodic structure of the active layer.
Further refinements of the invention are characterized in that a
further reflector arrangement is present between the active layer
and the metal film.
The vertical resonator is bounded by the reflector arrangement and
by the metal film in a preferred embodiment. The active layer is
preferably arranged between contact layers which adjoin said active
layer vertically with respect to the layer plane, and the spatial
periodic structure is formed in the surface of a covering layer
which is present between one of said contact layers and the metal
film. The metal film may be applied in a recess of a contact. The
metal film also forms a contact.
The laser diode according to the invention uses a layer structure,
as is fundamentally known from conventional surface-emitting laser
diodes having a vertical resonator. This structure is modified such
that the radiation of light can take place by excitation of surface
modes.
BRIEF DESCRIPTION OF THE DRAWINGS
There follows a description of the laser diode according to the
invention using FIGS. 1 and 2, which each show an embodiment in an
oblique sectional view.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The laser diode according to the invention has a layer structure
with an active layer 3 between contact layers 2, 4 provided for
supplying power to the active layer 3. The entire layer arrangement
is expediently grown onto a substrate 1. The spatial periodic
structure necessary for the excitation of the surface modes is
formed, for example by etching, in the surface of the semiconductor
material. In the exemplary embodiment in FIG. 1, this surface is
formed by the surface of a covering layer 10, which is grown onto
the upper contact layer 4. A thin metal film 5, for example made of
aluminum, gold or silver, is deposited on this structured surface.
The thickness d5 of this metal film 5 can, for example, be so small
that the metal film 5 is semitransparent. Typical thicknesses d5 of
the metal film 5 are 0.01 .mu.m to 0.1 .mu.m.
Further dimensions of this structure of the surface which govern
the excitation of the surface modes are illustrated in FIG. 1. What
are essential are the length of a period Lg, the minimum distance a
of the metal film 5 from the active layer 3 and the height h, that
is to say the difference between the minimum distance and the
maximum distance of the semiconductor surface coated with the metal
film 5 from the active layer 3.
A vertical resonator is formed in this laser diode by arranging
reflectors above and below the active layer 3 for producing a
resonance condition in the direction extending vertically with
respect to the layer planes. In the exemplary embodiment in FIG. 1,
a reflector arrangement 9 is provided between the substrate 1 and
the lower contact layer 2. The reflective metal film 5 forms the
upper reflector. The reflector arrangement 9 can comprise a single
layer or a layer sequence of successive semiconductor layers having
a different refractive index and, advantageously, in each case
having the thickness of a quarter-wavelength. It is particularly
advantageous in the case of the laser diode according to the
invention that a separate upper reflector arrangement can be
omitted, because its function can already be assumed by the metal
film 5. The covering layer 10 can then also be omitted and the
structure can be formed in the surface of the upper contact layer
4. The contacts which are necessary for applying the operating
current can be fitted, for example, in the manner indicated in the
case of a conductive substrate 1. A contact 7 is then present on
the top of the laser diode, which contact has a recess, in which
only the thin metal film 5 is applied, in the region of the
structure of the semiconductor surface. However, the metal film 5
can also be present across the whole area and it then suffices as a
contact for the electrical connection. The mating contact 8 is
situated on the bottom of the conductive substrate 1. The lower
contact layer 2 can then be omitted and current can be injected
into the active layer 3 through the reflector arrangement 9. If a
contact layer 2 is present, the mating contact can be fitted
directly on a surface of this contact layer over which surface
there is no growth or which surface is etched to be exposed. The
substrate 1 can then also be semi-insulating. In addition to the
structure shown, the surface of the metal film 5 can be covered
with a dielectric 6, as is indicated in FIG. 1 by the dot-dashed
line. As is described in European Patent Document EP-A-0 442 002,
such a layer of dielectric 6 serves to excite higher-order surface
modes. This dielectric 6 can also be designed as a layer sequence
of a plurality of different dielectrics.
FIG. 2 shows an alternative embodiment, in which a dedicated
reflector arrangement 19 is present above the active layer as well.
This reflector arrangement 19 is situated between the upper contact
layer 4 and the covering layer 10. In the case of a laser diode
which is built using the material system of GaAs, the substrate is,
for example, GaAs. The active zone 3 is likewise GaAs. The contact
layers 2, 4 are AlGaAs. The covering layer 10 can likewise be
AlGaAs. The reflector arrangements 9, 19 are advantageously a
sequence of layers made alternately of AlGaAs and AlAs. The active
layer 3 can also be designed as a quantum well structure. Using the
material system of GaAs, an active layer 3 made of a layer sequence
of layers made alternately of GaAs and InGaAs is then particularly
advantageous. InGaAs has a smaller energy band gap than GaAs, with
the result that the reflector arrangements 9, 19 can then be layer
sequences of layers made alternately of AlAs and GaAs, and this
simplifies the epitaxial growth. In a simplified design of this
laser diode, the upper reflector arrangement and the covering layer
10 are omitted, and the spatial periodic structure of the surface
of the semiconductor material is formed in the top, facing away
from the active layer 3, of the upper contact layer 4. The upper
reflector arrangement 19 is advantageously a sequence of layers
having a different refractive index and in each case the thickness
of a quarter-wavelength, or with radiation produced in the active
layer.
A conventional surface-emitting laser diode radiates essentially
perpendicularly with respect to the surface. Sharp beam focusing of
the light radiation, as is carried out in the case of the laser
diode according to the invention, can be achieved in a conventional
laser diode only by additional optical measures, such as a lens.
Light emission in different adjustable directions can additionally
be achieved by means of surface mode emission using the laser diode
according to the invention. The arrangement of the surface
structure and the suitable selection of the dimensions specified
above mean that directed radiation can be carried out at specific
angles. In addition, the polarization plane of the emitted light
can be adjusted. Limiting the periodic structure by means of the
thicker upper contact 7 means that the region of radiation emission
can be laterally limited. The design according to the invention is
not restricted to the material system of GaAs. Since the
attenuation of the surface modes decreases with increasing
wavelength, the excitation and emission mechanism of the surface
modes is particularly effective, especially in the infrared. It is
necessary only for the grating period to be matched to the
wavelength. For a given wavelength of the radiation produced in the
active layer 3, the radiation direction is fixed by the grating
period (period length Lg). The radiation direction can therefore be
defined by the dimensioning of the periodic structure at the
surface and the selection of the composition of the semiconductor
material of the active layer 3. The periodic structure can be
formed, as shown in the figures, by trenches aligned parallel to
one another. There is no periodicity in the direction of these
trenches. Instead of this embodiment, any structure described in
European Patent Document EP-A-0 442 002 can be provided. In
particular, it can be a cross grating, in which two sets are
present, aligned perpendicularly with respect to one another, of
trenches which are arranged parallel to one another and are in each
case at equal distances from the nearest trenches. The structure is
then periodic in each direction in the plane of the layer
structure. The trenches can be replaced by sets, aligned in a
crosswise manner, of webs, or the like, which are aligned parallel
to one another and are in each case at equal distances from the
nearest webs. The profile of the trenches or webs can be
rectangular or rounded, pointed, sinusoidal or polygonal.
The laser diode according to the invention enables extremely
focused surface emission in a predeterminable direction for a
component structure which can be produced easily.
Although other modifications and changes may be suggested by those
skilled in the art, it is the intention of the inventor to embody
within the patent warranted hereon all changes and modifications as
reasonably and properly come within the scope of his contribution
to the art.
* * * * *